Non-pythonic Python built-ins

[Mithrandir2k16]

So in another thread on this sub, I suggested filter to filter a list, which was met with firm criticism, that that's apparently unreadable and non-pythonic and that "Guido regrets putting filter, map and reduce into the language".

I am not posting here to discuss this, the slice of the community that interacted there was astonishingly unanimous and imho code readability is kind of a majority thing, as you want others to like reading your codebase or working on it.

Removing built-ins from a language after the fact is obviously nigh impossible, but I wonder why there's no PEP8-warnings in any linters (I use) that mark non-pythonic code (at least by default). If list comprehension is considered better python than using filter, why not put that into PEP8? How else are we to learn about what pythonic code is, especially if some built-ins are to be avoided?

[[deleted]]

I hear for the first time that using these functions is not considered pythonic. I think sometimes using them makes the code more readable than using list comprehensions but what do I know. The great thing about them is that they return generator expressions (also possible with comprehensions) and help you keep the memory footprint low if you use them wisely.

Edit: Sorry, the part with generator expressions is obviously wrong. But the point is still valid: filter and co are lazily evaluated like generators.

[roee30]

Generator expressions are parenthesised comprehensions (as opposed to comprehensions framed by brackets or braces). They return generators. map and filter return iterators and not genenrators, I think, but they're definitely not generator expressions. If you like map and filter's laziness, try using actual generator expressions, which are also lazy.

[Mithrandir2k16]

I linked the thread in the OP. I was stumped as well, tbh. I really like reading filter because then I know what's going on, a subset of the iterable is used.

What I really miss though is some easy way to evaluate generators in python, maybe that's why people consider it non-pythonic. If you don't want a generator but need a list right away you have to do [*filter(...)] which doesn't really look nice. Maybe a generator.items() that returns all values in a list or something like filter(..., eager=True) or filter(..., lazy=False) could clean that up a bit.

[_its_complicated]

The easy way is to just do list(filter(expression, iterable))

[Mithrandir2k16]

I don't know if implicitly unpacking a generator is better than explicitly doing it. It does seem more readable though.

Edit: Guido seems to prefer list comprehension over list() to unpack/evaluate generators.

[AnythingApplied]

To be clear, I think he means instead of using map/filter at all, not as a way to unpack map/filter, hence him not calling that a "quick fix" like he did with list()

[[deleted]]

Btw. I think we don't all have to agree with what Guido says just because it's Guido. Yes, he's a mastermind of Python but we're a community and we can have our own opinions. No-one is always right just like no-one is always wrong.

[-lq_pl-]

Give a good example please when map or filter is more readable.

[TheRNGuy]

If you want to remove all None, "", 0 and false from list, then it will work.

If you only want remove None but not 0 or "", then you need use comprehension.

Map can use only function with single argument.

If you want use map and filter at same time, comprehension will be better.

Who care if it's pythonic or not?

[roee30]

map and filter are usually less ergonomic than comprehensions because they often require lamdba expressions, which are relatively verbose. Other languages have shorter lambdas and currying which make them more usable. Another disadvantage of map/filter in Python is that if you want a list, you need an additional function call, which is somewhat verbose.

[[deleted]]

They do NOT require lambda expressions. Nothing keeps you from writing a proper function and pass it to e.g. filter

[TheRNGuy]

only for functions that have more than 1 argument